His friends used to call him `` Hoss , '' as in Hoss Cartwright from the TV show `` Bonanza . '' At 6 ' 2 '' and roughly 380 pounds , Mark Rucker once resembled the big , friendly character .

Now , they call him `` The Beast . ''

The nickname is apt . Since February 2011 , Rucker has run his first 5K , his first 10K , his first half-marathon and his first marathon . He 's completed an Olympic-distance triathlon and lost more than 100 pounds . And on August 26 , he 'll participate in his first full-length Ironman competition in Louisville , Kentucky .

Like they say , he 's a beast .

`` What he does after this Ironman , I do n't know , '' his wife , Annita Rucker , said with a laugh . `` I hope he can find something to focus all this energy on . ''

From Rucker 's DailyMile blog : April 18 , 2011 -- `` First day of the Couch to 5K program . That was not good . But at least I did the whole workout '' -LRB- 1.98 miles / 32 minutes / 16:10 pace -RRB-

Change is a funny thing , Rucker says . Often , the desire to change grows over time . A series of events leads to an `` a ha moment , '' when desire must meet with the proper tools and the right inspiration .

In the summer of 2010 , Rucker , of Lexington , Kentucky , and his family went to Dollywood in Tennessee . His daughter was 11 at the time , a `` little daredevil , '' and wanted to ride all the roller coasters . Unfortunately , Rucker could n't fit on any of them with her .

`` She was devastated ; I was crushed , '' Rucker said . `` But even that was n't enough to get me started on the journey . I guess I just did n't know how to do it . ''

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In January 2011 , he reconnected with an old elementary school friend , Anita Mills , and the two began talking on Facebook , discussing Mills ' 240-pound weight loss .

Her transformation was his inspiration . But he still was n't ready to change .

After weighing in at about 365 pounds , he stopped stepping on the scale . He was diagnosed with sleep apnea and put on medication for high blood pressure . He feared that he was diabetic but would n't visit his doctor .

The day after the 2011 Super Bowl , Rucker woke up in pain . Once again , he had overindulged the night before , and his digestive system revolted . He was tired , sick and unhappy .

`` Something clicked , '' he said . `` I realized that if I kept doing it , I would significantly shorten my life . ''

Rucker took Mills ' dieting hints to heart and cut out sugary drinks . He dropped his two-liter-a-day soda habit and picked up water . He stopped ordering McDonald 's McGriddles for breakfast and eating peanut M&M s by the pound . He threw away his Cheez-Its .

`` It 's hard to say what my daily -LRB- calorie -RRB- intake was , '' he said , looking back . `` I did it to myself . I was really unhappy with the way my life was , and I think food was that comfort for me . ''

June 19 , 2011 -- `` Last day of Couch 2 5K . I think I 'll call it The Father 's Day Beastly 5K . I was the only competitor and I finished in 1st place . I ca n't even begin to explain how I feel right now . And no one or no thing can ever take this away from me . I AM a runner . I AM an achiever . I AM a Beast . On to Bridge 2 10K !!! ''

Rucker 's job as a real estate attorney kept him sedentary . So he started to walk on his lunch break , using his iPhone to post his distance on DailyMile.com . The site shared his progress on Twitter and Facebook . Friends posted replies that the site 's app read aloud to Rucker through his headphones during workouts .

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`` That was a huge motivator to me , '' he said . `` Even though I was by myself , I still had people to encourage me . ''

He ran his first official 5K race , the Great Buffalo Chase , on July 4 , 2011 , in 39 minutes . Less than a month later , he tackled a 10K , finishing dead last but finishing all the same . His blog that night complained about the cross-country course 's hills but promised to begin training for a half-marathon the next day .

`` The focus he has , the drive he has ... it 's so refreshing , '' Annita Rucker said . `` It 's the old Mark I did n't even know -- probably the Mark from law school . ''

The Ruckers married in October 2000 . For 11 years , Annita Rucker watched the man she married -- the dreamer , the achiever -- struggle to maintain his optimism while grappling with a shrinking housing market and a growing body .

Their son and daughter -- two children from Rucker 's first marriage -- came to visit often , and Annita Rucker found herself entertaining the young kids while her husband remained stationary .

`` I used to complain that he was living life on the sidelines , never participating , '' she said . `` Now , he 's so active with them . Last year , my father had Parkinson 's and was hospitalized for 10 weeks . Mark stepped up to the plate and did all the cooking , the laundry , everything . Before this , that never would have happened . ''

`` My wife jokes , ` I 've got a brand new husband , ' '' Rucker said with a long laugh . `` I think she 's a lot happier with me ... because I 'm much happier . ''

August 18 , 2011 -- `` Three mile walk at work on my lunch break . Some days I got ta dig down deep to find the motivation . Some days it 's really hard . Today is one of those days . ''

Rucker is now training for his first Ironman competition . A typical week includes 4:30 a.m. swims , 6-mile runs after work and hours of cycling on Saturday and Sunday . At 260 pounds , he 's stopped focusing on losing weight and started focusing on building muscle .

There are good and bad days . Some blog posts sing of the serotonin rushing through his brain . Others show his discouragement of a bad swim or a slow run . He 's a beast , but one who feels pain .

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Still , it 's amazing , even to him , that a guy who less than two years ago got winded walking up a flight of stairs can push himself this far , this fast .

`` I 'm the guy in the overalls -LRB- who 's -RRB- shoveling the coal in the train , '' he said . `` I do n't know exactly where it 's going , but I 'm going to do everything I can to keep it moving . ''

February 18 , 2012 -- `` Woot woot !! I 'm a marathoner !! '' -LRB- 26.4 miles / 6 hours , 13 minutes / 14:07 pace -RRB-

Rucker has rejoined the social world . He volunteers at the Red Cross and is involved in his local Rotary chapter . This year , his family went back to Dollywood and rode all the rides together .

Rucker wants to become a motivational speaker , to be that inspiration for others that Mills was for him . Possible title for his speech : `` Be the Beast that you can be . ''

`` When I was so overweight , I felt so dead to everything , '' Rucker said . `` There was this little voice in my head that said , for so long , ` This is the best your life is ever going to be . ' And that voice is gone . I 've extinguished that voice . ''

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Mark Rucker lost more than 100 pounds by changing his diet and racing

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Rucker will compete in his first Ironman competition on August 26

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He used DailyMile.com and the iPhone app to track his workout progress